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Internet Engineering Task Force (IETF)                     R. Alimi, Ed.Request for Comments: 6392                                        GoogleCategory: Informational                                   A. Rahman, Ed.ISSN: 2070-1721                         InterDigital Communications, LLC                                                            Y. Yang, Ed.                                                         Yale University                                                            October 2011A Survey of In-Network Storage SystemsAbstract   This document surveys deployed and experimental in-network storage   systems and describes their applicability for the DECADE (DECoupled   Application Data Enroute) architecture.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6392.Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Alimi, et al.                 Informational                     [Page 1]

RFC 6392                      DECADE Survey                 October 2011Table of Contents1. Introduction ....................................................32. Survey Overview .................................................32.1. Terminology and Concepts ...................................32.2. Historical Context .........................................33. In-Network Storage System Components ............................53.1. Data Access Interface ......................................53.2. Data Management Operations .................................53.3. Data Search Capability .....................................63.4. Access Control Authorization ...............................63.5. Resource Control Interface .................................63.6. Discovery Mechanism ........................................73.7. Storage Mode ...............................................74. In-Network Storage Systems ......................................74.1. Amazon S3 ..................................................74.2. BranchCache ................................................94.3. Cache-and-Forward Architecture ............................114.4. Cloud Data Management Interface ...........................124.5. Content Delivery Network ..................................144.6. Delay-Tolerant Network ....................................164.7. Named Data Networking .....................................184.8. Network of Information ....................................194.9. Network Traffic Redundancy Elimination ....................224.10. OceanStore ...............................................234.11. P2P Cache ................................................244.12. Photo Sharing ............................................264.13. Usenet ...................................................284.14. Web Cache ................................................294.15. Observations Regarding In-Network Storage Systems ........315. Storage and Other Related Protocols ............................325.1. HTTP ......................................................325.2. iSCSI .....................................................335.3. NFS .......................................................345.4. OAuth .....................................................365.5. WebDAV ....................................................375.6. Observations Regarding Storage and Related Protocols ......396. Conclusions ....................................................407. Security Considerations ........................................408. Contributors ...................................................409. Acknowledgments ................................................4110. Informative References ........................................41Alimi, et al.                 Informational                     [Page 2]

RFC 6392                      DECADE Survey                 October 20111.  Introduction   DECADE (DECoupled Application Data Enroute) is an architecture that   provides applications with access to provider-based in-network   storage for content distribution (hereafter referred to as only   "in-network storage" in this document).  With access to in-network   storage, content distribution applications can be designed to place   less load on network infrastructure.  As a simple example, a peer of   a Peer-to-Peer (P2P) application may upload to other peers through   its in-network storage, saving its usage of last-mile uplink   bandwidth.  See [1] for further discussion.   A major motivation for DECADE is the substantial increase in capacity   and reduction in cost offered by storage systems.  For example, over   the last two decades, there has been at least a 30-fold increase in   the amount of storage that a customer can get for a given price (for   flash memory and hard disk drives) [2] [3] [4].   High-capacity and low-cost in-network storage devices introduce   substantial opportunities.  One example of in-network storage is   content caches supporting Web and P2P content.  DECADE differs from   existing content caches whose control fully resides with the owners   of the caching devices in that DECADE also allows applications to   control access to their allocated in-network storage, as well as the   resources consumed while accessing that storage (bandwidth,   connections, storage space).  While designed in the context of P2P   applications, DECADE may be useful to other applications as well.   This document provides details on deployed and experimental   in-network storage solutions, and evaluates their suitability for   DECADE.   We note that the survey presented in this document is only   representative of the research in this area.  Rather than trying to   enumerate an exhaustive list, we have chosen some typical techniques   that lead to derivative works.2.  Survey Overview2.1.  Terminology and Concepts   This document uses terms defined in [1].2.2.  Historical Context   In-network storage has been used previously in numerous scenarios to   reduce network traffic and enable more efficient content   distribution.  This section presents a brief history of content   distribution techniques and illustrates how DECADE relates to pastAlimi, et al.                 Informational                     [Page 3]

RFC 6392                      DECADE Survey                 October 2011   approaches.  Systems have been developed with particular use cases in   mind.  Thus, this survey is not meant to point out shortcomings of   existing solutions, but rather to indicate where certain capabilities   required in DECADE [5] are not provided by existing systems.   In the early stage of Internet development, most Web content was   stored at a central server, and clients requested Web content from   the central server.  In this architecture, the central server was   required to provide a large amount of bandwidth.  As more and more   users access Web content, a central server can become overloaded.   The use of Web caches is one technique to reduce load on a central   server.  Web caches store frequently requested content and provide   bandwidth for serving the content to clients.   The ongoing growth of broadband technology in the worldwide market   has been driven by the hunger of customers for new multimedia   services as well as Web content.  In particular, the use of audio and   video streaming formats has become common for delivery of rich   information to the public, both residential and business.   To overcome this challenge of massive multimedia consumption, just   installing more Web caches will not be enough.  Moving content closer   to the consumer results in greater network efficiency, improved   Quality of Service (QoS), and lower latency, while facilitating   personalization of content through broadband content applications.   In these edge technologies, Content Delivery Networks (CDNs) are a   representative technique.  CDNs are based on a large-scale   distributed network of servers located closer to customers for   efficient delivery of digital content, including various forms of   multimedia content.   Although CDNs are an effective means of information access and   delivery, there are two barriers to making CDNs a more common   service: cost and replication integrity.  Deploying a CDN with its   associated infrastructure is expensive.  A CDN also requires   administrative control over nodes with large storage capacity at   geographically dispersed locations with adequate connectivity.  CDNs   can be scalable, but due to this administrative and cost overhead,   they are not rapidly deployable for the common user.   The emergence and maturation of P2P has allowed improvements to many   network applications.  P2P allows the use of client resources, such   as CPU, memory, storage, and bandwidth, for serving content.  This   can reduce the amount of resources required by a content provider.   Multimedia content delivery using various P2P or peer-assisted   frameworks has been shown to greatly reduce the dependence on CDNs   and central content servers.  However, the popularity of P2P   applications has resulted in increased traffic on ISP networks.  P2PAlimi, et al.                 Informational                     [Page 4]

RFC 6392                      DECADE Survey                 October 2011   caches (both transparent and non-transparent) have been introduced as   a way to reduce the burden.  Though they can be effective in reducing   traffic in certain areas of ISP networks, P2P caches have their   shortcomings.  In particular, they are application-dependent and thus   difficult to keep up to date with new and evolving P2P application   protocols.  Second, applications may benefit from explicit control of   in-network storage, which P2P caches do not provide.  See [1] for   further discussion.   DECADE aims to provide a standard protocol allowing P2P applications   (including content providers) to make use of in-network storage to   reduce the traffic burden on ISP networks, while enabling P2P   applications to control access to content they have placed in   in-network storage.3.  In-Network Storage System Components   Before surveying individual technologies, we describe the basic   components of in-network storage.  For consistency and for ease of   comparison, we use the same model to evaluate each storage technology   in this document.   Note that the network protocol(s) used by a given storage system are   also an important part of the design.  We omit details of particular   protocol choices in this document.3.1.  Data Access Interface   A set of operations is made available to a user for accessing data in   the in-network storage system.  Solutions typically allow both read   and write operations, though the mechanisms for doing so can differ   drastically.3.2.  Data Management Operations   Storage systems may provide users the ability to manage stored   content.  For example, operations such as delete and move may be   provided to users.  In this survey, we focus on data management   operations that are provided to users and omit those provided to   system administrators.Alimi, et al.                 Informational                     [Page 5]

RFC 6392                      DECADE Survey                 October 20113.3.  Data Search Capability   Some storage systems may provide the capability to search or   enumerate content that has been stored.  In this survey, we focus on   search capabilities that are provided to users and omit those   provided to system administrators.  An example of a search would be   to find the list of items stored by a given user over a given period   of time.3.4.  Access Control Authorization   Storage systems typically allow a user, content owner, or some other   entity to define the access policies for the in-network storage   system.  The in-network storage system then checks the authorization   of a user before it stores or retrieves content.  We define three   types of access control authorization: public-unrestricted, public-   restricted, and private.   "Public-unrestricted" refers to content on an in-network storage   system that is widely available to all clients (i.e., without   restrictions).  An example is accessing Wikipedia on the Web, or   anonymous access to FTP sites.   "Public-restricted" refers to content on an in-network storage system   that is available to a restricted (though still potentially large)   set of clients, but that does not require any confidential   credentials from the client.  An example is some content (e.g., a TV   show episode) on the Internet that can only be viewable in selected   countries or networks (i.e., white/black lists or black-out areas).   "Private" refers to content on an in-network storage system that is   only made available to one or more clients presenting the required   confidential credentials (e.g., password or key).  This content is   not available to anyone without the proper confidential access   credentials.   Note that a combination of access control types may be applicable for   a given scenario.  For example, the retrieval (read) of content from   an in-network storage system may be public-unrestricted, but the   storage (write) to the same system may be private.3.5.  Resource Control Interface   This is the interface through which users manage the resources on   in-network storage systems that can be used by other peers, e.g., the   bandwidth or connections.  The storage system may also allow users to   indicate a time for which resources are granted.Alimi, et al.                 Informational                     [Page 6]

RFC 6392                      DECADE Survey                 October 20113.6.  Discovery Mechanism   Users use the discovery mechanism to find the location of in-network   storage, find an access interface or resource control interface, or   find other interfaces of in-network storage.3.7.  Storage Mode   Storage systems may use the following modes of storage: file system,   object-based, or block-based.   A file system typically organizes files into a hierarchical tree   structure.  Each level of the hierarchy normally contains zero or   more directories, each with zero or more files.  A file system may   also be flat or use some other organizing principle.   We define an object-based storage mode as one that stores discrete   chunks of data (e.g., IP datagrams or another type of aggregation   useful to an application) without a pre-defined hierarchy or   meta-structure.   We define a block-based storage mode as one that stores a raw   sequence of bytes, with a client being able to read and/or write data   at offsets within that sequence.  Data is typically accessed in   blocks for efficiency.  A common example for this storage mode is raw   access to a hard disk.   In this survey, we define "storage mode" to refer to how data is   structured within the system, which may not be the same as how it is   accessed by a client.  For example, a caching system may cache   objects with hierarchical names, but may internally use an object-   based storage mode.4.  In-Network Storage Systems   This section surveys in-network storage systems using the methodology   defined above.  The survey includes some systems that are widely   deployed today, some systems that are just being deployed, and some   experimental systems.  The survey covers both traditional client-   server architectures and P2P architectures.  The surveyed systems are   listed in alphabetical order.  Also, for each system, a brief   explanation of the relevance to DECADE is given.4.1.  Amazon S3   Amazon S3 (Simple Storage Service) [6] provides an online storage   service using Web (HTTP) interfaces.  Users create buckets, and each   bucket can contain stored objects.  Users are provided an interfaceAlimi, et al.                 Informational                     [Page 7]

RFC 6392                      DECADE Survey                 October 2011   through which they can manage their buckets.  Amazon S3 is a popular   backend storage service for other services.  Other related storage   services are the Blob Service provided by Windows Azure [7], Google   Storage for Developers [8], and Dropbox [9].4.1.1.  Applicability to DECADE   Amazon S3 is a very widely used (deployed) example of in-network   storage.  Amazon S3 leases the storage to third-party companies for   disparate services.  In particular, Amazon S3 has a rich model for   authorization (using signed queries) to integrate with a wide variety   of use cases.  A focus for Amazon S3 is scalability.  Particular   simplifications that were made are the absence of a general,   hierarchical namespace and the inability to update the contents of   existing data.4.1.2.  Data Access Interface   Users can read and write objects.4.1.3.  Data Management Operations   Users can delete previously stored objects.4.1.4.  Data Search Capability   Users can list contents of buckets to find objects matching desired   criteria.4.1.5.  Access Control Authorization   All methods of access control are supported for clients: public-   unrestricted, public-restricted, and private.   For example, access to stored objects can be restricted by an owner,   a list of other Amazon S3 Web Service users, or all Amazon S3 Web   Service users; or can be open to all users (anonymous access).   Another option is for the owner to generate and sign a query (e.g., a   query to read an object) that can be used by any user until an owner-   defined expiration time.4.1.6.  Resource Control Interface   Not provided.Alimi, et al.                 Informational                     [Page 8]

RFC 6392                      DECADE Survey                 October 20114.1.7.  Discovery Mechanism   Users are provided a well-known DNS name (either a default provided   by Amazon S3, or one customized by a particular user).  Users   accessing S3 storage use DNS to discover an IP address where S3   requests can be sent.4.1.8.  Storage Mode   Object-based, with the extension that objects can be organized into   user-defined buckets.4.2.  BranchCache   BranchCache [10] is a feature integrated into Windows (Windows 7 and   Windows Server 2008R2) that aims to optimize enterprise branch office   file access over WAN links.  The main goals are to reduce WAN link   utilization and improve application responsiveness by caching and   sharing content within a branch while still maintaining end-to-end   security.  BranchCache allows files retrieved from the Web servers   and file servers located in headquarters or data centers to be cached   in remote branch offices, and shared among users in the same branch   accessing the same content.  BranchCache operates transparently by   instrumenting the HTTP and Server Message Block (SMB) components of   the networking stack.  It provides two modes of operation:   Distributed Cache and Hosted Cache.   In both modes, a client always contacts a BranchCache-enabled content   server first to get the content identifiers for local search.  If the   content is cached locally, the client then retrieves the content   within the branch.  Otherwise, the client will go back to the   original content server to request the content.  The two modes differ   in how the content is shared.   In the Hosted Cache mode, a locally provisioned server acts as a   cache for files retrieved from the servers.  After getting the   content identifiers, the client first consults the cache for the   desired file.  If it is not present in the cache, the client   retrieves it from the content server and sends it to the cache for   storage.   In the Distributed Cache mode, a client first queries other clients   in the same network using the Web Services Discovery multicast   protocol [11].  As in the Hosted Cache mode, the client retrieves the   file from the content server if it is not available locally.  After   retrieving the file (either from another client or the content   server), the client stores the file locally.Alimi, et al.                 Informational                     [Page 9]

RFC 6392                      DECADE Survey                 October 2011   The original content server always authorizes requests from clients.   Cached content is encrypted such that clients can decrypt the data   only using keys derived from metadata returned by the content server.   In addition to instrumenting the networking stack at clients, content   servers must also support BranchCache.4.2.1.  Applicability to DECADE   BranchCache is an example of an in-network storage system primarily   targeted at enterprise networks.  It supports a P2P-like mode   (Distributed Cache) as well as a client-server mode (Hosted Cache).   Integration into the Microsoft OS will ensure wide distribution of   this in-network storage technology.4.2.2.  Data Access Interface   Clients transparently retrieve (read) data from a cache (on a client   or a Hosted Cache), since BranchCache operates by instrumenting the   networking stack.  In the Hosted Cache mode, clients write data to   the Hosted Cache once it is retrieved from the content server.4.2.3.  Data Management Operations   Not provided.4.2.4.  Data Search Capability   Not provided.4.2.5.  Access Control Authorization   The access control method for clients is private.  For example,   transferred content is encrypted, and can only be decrypted by keys   derived from data received from the original content server.  Though   data may be transferred to unauthorized clients, end-to-end security   is maintained by only allowing authorized clients to decrypt the   data.4.2.6.  Resource Control Interface   The storage capacity of caches on the clients and Hosted Caches is   configurable by system administrators.  The Hosted Cache further   allows configuration of the maximum number of simultaneous client   accesses.  In the Distributed Cache mode, exponential back-off and   throttling mechanisms are utilized to prevent reply storms of popular   content requests.  The client will also spread data-block access   among multiple serving clients that have the content (complete or   partial) to improve latency and provide some load balancing.Alimi, et al.                 Informational                    [Page 10]

RFC 6392                      DECADE Survey                 October 20114.2.7.  Discovery Mechanism   The Distributed Cache mode uses multicast for discovery of other   clients and content within a local network.  Currently, the Hosted   Cache mode uses policy provisioning or manual configuration of the   server used as the Hosted Cache.  In this mode, the address of the   server may be found via DNS.4.2.8.  Storage Mode   Object-based.4.3.  Cache-and-Forward Architecture   Cache-and-Forward (CNF) [12] is an architecture for content delivery   services for the future Internet.  In this architecture, storage can   be exploited on nodes within the network, either directly on routers   or deployed near the routers.  CNF is based on the concept of store-   and-forward routers with large storage, providing for opportunistic   delivery to occasionally disconnected mobile users and for in-network   caching of content.  The proposed CNF protocol uses reliable hop-by-   hop transfer of large data files between CNF routers in place of an   end-to-end transport protocol such as TCP.4.3.1.  Applicability to DECADE   CNF is an example of an experimental in-network storage system that   would require storage space on (or near) a large number of routers in   the Internet if it was deployed.  As the name of the system implies,   it would provide short-term caching and not long-term network   storage.4.3.2.  Data Access Interface   Users implicitly store content at CNF routers by requesting files.   End hosts read content from in-network storage by submitting queries   for content.4.3.3.  Data Management Operations   Not provided.4.3.4.  Data Search Capability   Not provided.Alimi, et al.                 Informational                    [Page 11]

RFC 6392                      DECADE Survey                 October 20114.3.5.  Access Control Authorization   The access control method is public-restricted (to any client that is   part of the CNF network).4.3.6.  Resource Control Interface   Not provided.4.3.7.  Discovery Mechanism   A query including a location-independent content ID is sent to the   network and routed to a CNF router, which handles retrieval of the   data and forwarding to the end host.4.3.8.  Storage Mode   Object-based, with objects representing individual files.  The   architecture proposes to cache large files in storage within the   network, though objects could be made to represent smaller chunks of   larger files.4.4.  Cloud Data Management Interface   The Cloud Data Management Interface (CDMI) is a specification to   access and manage cloud storage.  CDMI is specified by the Storage   Networking Industry Association (SNIA).   CDMI is a functional interface that applications can use to create,   retrieve, update, and delete data elements from the cloud.  As part   of this interface, the client will be able to discover the   capabilities of the cloud storage offering and use this interface to   manage containers and the data that is placed in them.  In addition,   metadata can be set on containers and their contained data elements   through this interface [13].   CDMI follows a traditional client-server model, and operates over an   HTTP interface using the Representational State Transfer (REST)   model.  Similar to Amazon S3 buckets (seeSection 4.1), users may   create containers in which data objects may be stored.  Even though   data objects may be accessed via a user-defined name within a   container, it is also possible to access data objects via a storage-   defined Object ID, which is provided in the response upon creation of   a data object.Alimi, et al.                 Informational                    [Page 12]

RFC 6392                      DECADE Survey                 October 20114.4.1.  Applicability to DECADE   CDMI is an important initiative to standardize storage interfaces for   cloud services, which are rapidly becoming an important type of   storage service.  In particular, it specifies a set of operations for   creating, reading, writing, and managing data objects at a remote   server (or set of servers) via HTTP.4.4.2.  Data Access Interface   Users can read and write data objects, and also update data in   existing data objects.  CDMI data objects are sent on the wire   embedded as a field in a JavaScript Object Notation (JSON) object.   The protocol also defines interfaces in which the contents of data   objects can be written via simple HTTP GET/PUT operations.4.4.3.  Data Management Operations   Users can delete already-existing data objects.  The create operation   also supports modes in which the created object is copied or moved   from an existing data object.   Data system metadata also allows users to configure policies   regarding time-to-live, after which a data object is automatically   deleted, as well as the redundancy with which a data object is   stored.4.4.4.  Data Search Capability   Users may list the contents of containers to locate data objects   matching any desired criteria.4.4.5.  Access Control Authorization   All methods of access control for clients are supported: public-   unrestricted, public-restricted, and private.   In particular, CDMI allows access to data objects to be protected by   Access Control Lists (ACLs) that can allow or restrict access based   on user name, group, administrative status, or whether a user is   authenticated or anonymous.4.4.6.  Resource Control Interface   CDMI supports attributes 'cdmi_max_latency' and 'cdmi_max_throughput'   (set at either the level of containers, or a specific data object),   which control the level of service offered to any users accessing a   particular data object.Alimi, et al.                 Informational                    [Page 13]

RFC 6392                      DECADE Survey                 October 20114.4.7.  Discovery Mechanism   Users are provided a well-known DNS name.  The DNS name is resolved   to determine the IP address to which requests may be sent.4.4.8.  Storage Mode   Object-based, with the extension that objects can be organized into   user-defined containers.4.5.  Content Delivery Network   A CDN provides services that improve performance by minimizing the   amount of data transmitted through the network, improving   accessibility, and maintaining correctness through content   replication.  CDNs offer fast and reliable applications and services   by distributing content to cache or edge servers located close to   users.  See [14] for an additional taxonomy and survey.   A CDN has some combination of content delivery, request routing,   distribution, and accounting infrastructures.  The content-delivery   infrastructure consists of a set of edge servers (also called   surrogates) that deliver copies of content to end users.  The   request-routing infrastructure is responsible for directing client   requests to appropriate edge servers.  It also interacts with the   distribution infrastructure to keep an up-to-date view of the content   stored in the CDN caches.  The distribution infrastructure moves   content from the origin server to the CDN edge servers and ensures   consistency of content in the caches.  The accounting infrastructure   maintains logs of client accesses and records the usage of the CDN   servers.  This information is used for traffic reporting and usage-   based billing.   In practice, a CDN typically hosts static content including images,   video, media clips, advertisements, and other embedded objects for   Web viewing.  A focus for CDNs is the ability to publish and deliver   content to end users in a reliable and timely manner.  A CDN focuses   on building its network infrastructure to provide the following   services and functionalities: storage and management of content;   distribution of content among surrogates; cache management; delivery   of static, dynamic, and streaming content; backup and disaster   recovery solutions; and monitoring, performance measurement, and   reporting.   Examples of existing CDNs are Akamai, Limelight, and CloudFront.Alimi, et al.                 Informational                    [Page 14]

RFC 6392                      DECADE Survey                 October 2011   The following description uses the term "content provider" to refer   to the entity purchasing a CDN service, and the term "client" to   refer to the subscriber requesting content via the CDN from the   content provider.4.5.1.  Applicability to DECADE   CDNs are a very widely used (deployed) example of in-network storage   for multimedia content.  The existence and operation of the storage   system are totally transparent to the end user.  CDNs typically   require a strong business relationship between the content providers   and content distributors, and often the business relationship extends   to the ISPs.4.5.2.  Data Access Interface   A CDN is typically a closed system, and generally provides only a   read (retrieve) access interface to clients.  A CDN typically does   not provide a write (store) access interface to clients.  The content   provider can access network edge servers and store content on them,   or edge servers can retrieve content from content providers.  Client   nodes can only retrieve content from edge servers.4.5.3.  Data Management Operations   A content provider can manage the data distributed in different cache   nodes, such as moving popular data objects from one cache node to   another cache node, or deleting rarely accessed data objects in cache   nodes.  User nodes, however, have no right to perform these   operations.4.5.4.  Data Search Capability   A content provider can search or enumerate the data each cache node   stores.  User nodes cannot perform search operations.4.5.5.  Access Control Authorization   All methods of access control (for reading) are supported for   clients: public-unrestricted, public-restricted, and private.  Some   CDN edge servers allow usage of HTTP basic authentication with the   origin server or restrictions by IP address, or they can use a token-   based technique to allow the origin server to apply its own   authorization criteria.   As mentioned previously, clients typically cannot write to the CDN.   Writing is typically a private operation for the content providers.Alimi, et al.                 Informational                    [Page 15]

RFC 6392                      DECADE Survey                 October 20114.5.6.  Resource Control Interface   Not provided.4.5.7.  Discovery Mechanism   Content providers can directly find internal CDN cache nodes to store   content, since they typically have an explicit business relationship.   Clients can locate CDN nodes through DNS or other redirection   mechanisms.4.5.8.  Storage Mode   Though the addressing of objects uses URLs that typically refer to   objects in a hierarchical fashion, the storage mode is typically   object-based.4.6.  Delay-Tolerant Network   The Delay-Tolerant Network (DTN) [15] is an evolution of an   architecture originally designed for the Interplanetary Internet.   The Interplanetary Internet is a communication system envisioned to   provide Internet-like services across interplanetary distances in   support of deep space exploration.  The DTN architecture can be   utilized in various operational environments characterized by severe   communication disruptions, disconnections, and high delays (e.g., a   month-long loss of connectivity between two planetary networks   because of high solar radiation due to sun spots).  The DTN   architecture is thus suitable for environments including deep space   networks, sensor-based networks, certain satellite networks, and   underwater acoustic networks.   A key aspect of the DTN is a store-and-forward overlay layer called   the "Bundle Protocol" or "Bundle Layer", which exists between the   transport and application layers [16].  The Bundle Layer forms a   logical overlay that employs persistent storage to help combat long-   term network interruptions by providing a store-and-forward service.   While traditional IP networks are also based on store-and-forward   principles, the amount of time of a packet being kept in "storage" at   a traditional IP router is typically on the order of milliseconds (or   less).  In contrast, the DTN architecture assumes that most Bundle   Layer nodes will use some form of persistent storage (e.g., hard   disk, flash memory, etc.) for DTN packets because of the nature of   the DTN environment.Alimi, et al.                 Informational                    [Page 16]

RFC 6392                      DECADE Survey                 October 20114.6.1.  Applicability to DECADE   The DTN is an example of an experimental in-network storage system   that would require fundamental changes to the Internet protocols.4.6.2.  Data Access Interface   Users implicitly cause content to be stored (until successfully   forwarded) at Bundle Layer nodes by initiating/terminating any   transaction that traverses the DTN.4.6.3.  Data Management Operations   Users can implicitly cause deletion of content stored at Bundle Layer   nodes via a "time-to-live" type of parameter that the user can   control (for transactions originating from the user).4.6.4.  Data Search Capability   Not provided.4.6.5.  Access Control Authorization   The access control method is public-restricted (to any client that is   part of the DTN) or private.4.6.6.  Resource Control Interface   Not provided.4.6.7.  Discovery Mechanism   A Uniform Resource Identifier (URI) approach is used as the basis of   the addressing scheme for DTN transactions (and subsequent store-and-   forward routing through the DTN network).4.6.8.  Storage Mode   Object-based.  DTN applications send data to the Bundle Layer, which   then breaks the data into segments.  These segments are then routed   through the DTN network, and stored in Bundle Layer nodes as required   (before being forwarded).Alimi, et al.                 Informational                    [Page 17]

RFC 6392                      DECADE Survey                 October 20114.7.  Named Data Networking   Named Data Networking (NDN) [17] is a research initiative that   proposes to move to a new model of addressing and routing for the   Internet.  NDN uses "named data"-based routing and forwarding, to   replace the current IP-address-based model.  NDN also uses name-based   data caching in the routers.   Each NDN Data packet will be assigned a content name and will be   cryptographically signed.  Data delivery is driven by the requesting   end.  Routers disseminate name-based prefix announcements by using   routing protocols such as Intermediate System to Intermediate System   (IS-IS) or the Border Gateway Protocol (BGP).  The requester will   send out an "Interest" packet, which identifies the name of the data   that it wants.  Routers that receive this Interest packet will   remember the interface it came from and will then forward it on a   name-based routing protocol.  Once an Interest packet reaches a node   that has the desired data, a named Data packet is sent back, which   carries both the name and content of the data, along with a digital   signature of the producer.  This named Data packet is then forwarded   back to the original requester on the reverse path of the Interest   packet [18].   A key aspect of NDN is that routers have the capability to cache the   named data.  If a request for the same data (i.e., same name) comes   to the router, then the NDN router will forward the named data stored   locally to fulfill the request.  The proponents of NDN believe that   the network can be designed naturally, matching data delivery   characteristics instead of communication between endpoints, because   data delivery has become the primary use of the network.4.7.1.  Applicability to DECADE   NDN is an example of an experimental in-network storage system that   would require storage space on a large number of routers in the   Internet.  Named Data packets would be kept in storage in the NDN   routers and provided to new requesters of the same data.4.7.2.  Data Access Interface   Users implicitly store content at NDN routers by requesting content   (the named Data packets) from the network.  Subsequent requests by   different users for the same content will cause the named Data   packets to be read from the NDN routers' in-network storage.Alimi, et al.                 Informational                    [Page 18]

RFC 6392                      DECADE Survey                 October 20114.7.3.  Data Management Operations   Users do not have the direct ability to delete content stored in the   NDN routers.  However, there will be some type of time-to-live   parameter associated with the named Data packets, though this has not   yet been specified.4.7.4.  Data Search Capability   Not provided.4.7.5.  Access Control Authorization   All methods of access control for clients are supported: public-   unrestricted, public-restricted, and private.   The basic security mechanism in NDN is for the sender to digitally   sign the content (the named Data packets) that it sends.  It is   envisioned that a complete access control system can be built on top   of NDN, though this has not yet been specified.4.7.6.  Resource Control Interface   Not provided.4.7.7.  Discovery Mechanism   Names are used as the basis of the addressing and discovery scheme   for NDN (and subsequent store-and-forward routing through the NDN   network).  NDN names are assumed to be hierarchical and to be able to   be deterministically constructed.  This is still an active area of   research.4.7.8.  Storage Mode   Object-based.  NDN sends named Data packets through the network.   These Data packets are routed through the NDN network and stored in   NDN routers.4.8.  Network of Information   Similar to NDN (seeSection 4.7), Network of Information (NetInf)   [19] is another information-centric approach in which the named data   objects are the basic component of the networking architecture.   NetInf is thus moving away from today's host-centric networkingAlimi, et al.                 Informational                    [Page 19]

RFC 6392                      DECADE Survey                 October 2011   architecture where the nodes in the network are the primary objects.   In today's network, the information objects are named relative to the   hosts they are stored on (e.g.,   http://www.example.com/information-object.txt).   The NetInf naming and security framework builds the foundation for an   information-centric security model that integrates security deeply   into the architecture.  In this model, trust is based on the   information itself.  Information objects (IOs) are given a unique   name with cryptographic properties.  Together with additional   metadata, the name can be used to verify the data integrity as well   as several other security properties, such as self-certification,   name persistency, and owner authentication and identification.  The   approach also gives some benefits over the security model in today's   host-centric networks, as it minimizes the need for trust in the   infrastructure, including the hosts providing the data, the channel,   or the resolution service.   In NetInf, the information objects are published into the network.   They are registered with a Name Resolution Service (NRS).  The NRS is   also used to register network locators that can be used to retrieve   data objects that represent the published IOs.  When a receiver wants   to retrieve an IO, the request for the IO is resolved by the NRS into   a set of locators.  These locators are then used to retrieve a copy   of the data object from the "best" available source(s).  NetInf is   open to use any type of underlying transport network.  The locators   can thus be a heterogeneous set, e.g., IPv4, IPv6, Medium Access   Control (MAC), etc.   NetInf will make extensive use of caching of information objects in   the network and will provide network functionality that is similar to   what overlay solutions such as CDNs and P2P distribution networks   (e.g., BitTorrent) provide today.4.8.1.  Applicability to DECADE   NetInf is an example of an experimental information-centric network   architecture that will require storage space for storage and caching   of information objects on a large number of NetInf nodes in the   Internet.Alimi, et al.                 Informational                    [Page 20]

RFC 6392                      DECADE Survey                 October 20114.8.2.  Data Access Interface   Users will publish IOs with specific IDs into the network.  This is   done by the client sending a register message to the NRS stating that   the IO with the specific ID is available.  When another user wishes   to retrieve the IO, they will use the given ID to make a request for   the IO.  The ID is then resolved by the NRS, and the IO is delivered   from a nearby in-network storage location.4.8.3.  Data Management Operations   Users do not have the direct ability to delete content stored in the   NetInf nodes.  However, there can be some type of time-to-live   parameter associated with the information objects, though this has   not yet been specified.4.8.4.  Data Search Capability   Not provided.4.8.5.  Access Control Authorization   All methods of access control for clients are supported: public-   unrestricted, public-restricted, and private.  The basic security   mechanism in NetInf is for the publisher to digitally sign the   content of the information object that it publishes.  It is   envisioned that a complete access control system can be built on top   of NetInf, though this has not yet been specified.4.8.6.  Resource Control Interface   Not provided.4.8.7.  Discovery Mechanism   NetInf IDs are used for naming and accessing information objects.   The IDs are resolved by the NRS into locators that are used for   routing and transport of data through the transport networks.  This   is still an active area of research.4.8.8.  Storage Mode   Object-based.  From an application perspective, NetInf can be used   for publishing entire files or chunks of files.  NetInf is agnostic   to the application perspective and treats everything as information   objects.Alimi, et al.                 Informational                    [Page 21]

RFC 6392                      DECADE Survey                 October 20114.9.  Network Traffic Redundancy Elimination   Redundancy Elimination (RE) is used for identifying and removing   repeated content from network transfers.  This technique has been   proposed to improve network performance in many types of networks,   such as ISP backbones and enterprise access links.  One example of an   RE proposal is SmartRE [20], proposed by Anand et al., which focuses   on network-wide RE.  In packet-level RE, forwarding elements are   equipped with additional storage that can be used to cache data from   forwarded packets.  Upstream routers may replace packet data with a   fingerprint that tells a downstream router how to decode and   reconstruct the packet based on cached data.4.9.1.  Applicability to DECADE   RE is an example of an experimental in-network storage system that   would require a large amount of associated packet processing at   routers if it was ever deployed.4.9.2.  Data Access Interface   RE is typically transparent to the user.  Writing into storage is   done by transferring data that has not already been cached.  Storage   is read when users transmit data identical to previously transmitted   data.4.9.3.  Data Management Operations   Not provided.4.9.4.  Data Search Capability   Not provided.4.9.5.  Access Control Authorization   The access control method is public-restricted (to any client that is   part of the RE network).  Note that the content provider still   retains control over which peers receive the requested data.  The   returned data is "compressed" as it is transferred within the   network.4.9.6.  Resource Control Interface   Not provided.  The content provider still retains control over the   rate at which packets are sent to a peer.  The packet size within the   network may be reduced.Alimi, et al.                 Informational                    [Page 22]

RFC 6392                      DECADE Survey                 October 20114.9.7.  Discovery Mechanism   No discovery mechanism is necessary.  Routers can use RE without the   users' knowledge.4.9.8.  Storage Mode   Object-based, with "objects" being data from packets transmitted   within the network.4.10.  OceanStore   OceanStore [21] is a storage platform developed at the University of   California, Berkeley, that provides globally distributed storage.   OceanStore implements a model where multiple storage providers can   pool resources together.  Thus, a major focus is on resiliency, self-   organization, and self-maintenance.   The protocol is resilient to some storage nodes being compromised by   utilizing Byzantine agreement and erasure codes to store data at   primary replicas.4.10.1.  Applicability to DECADE   OceanStore is an example of an experimental in-network storage system   that provides a high degree of network resilience to failure   scenarios.4.10.2.  Data Access Interface   Users may read and write objects.4.10.3.  Data Management Operations   Objects may be replaced by newer versions, and multiple versions of   an object may be maintained.4.10.4.  Data Search Capability   Not provided.4.10.5.  Access Control Authorization   Provided, but specifics for clients are unclear from the available   references.Alimi, et al.                 Informational                    [Page 23]

RFC 6392                      DECADE Survey                 October 20114.10.6.  Resource Control Interface   Not provided.4.10.7.  Discovery Mechanism   Users require an entry point into the system in the form of one   storage node that is part of OceanStore.  If a hostname is provided,   the address of a storage node may be determined via DNS.4.10.8.  Storage Mode   Object-based.4.11.  P2P Cache   Caching of P2P traffic is a useful approach to reduce P2P network   traffic, because objects in P2P systems are mostly immutable and the   traffic is highly repetitive.  In addition, making use of P2P caches   does not require changes to P2P protocols and can be deployed   transparently from clients.   P2P caches operate similarly to Web caches (Section 4.14) in that   they temporarily store frequently requested content.  Requests for   content already stored in the cache can be served from local storage   instead of requiring the data to be transmitted over expensive   network links.   Two types of P2P caches exist: transparent P2P caches and   non-transparent P2P caches.   For a transparent cache, once a P2P cache is established, the network   will transparently redirect P2P traffic to the cache, which either   serves the file directly or passes the request on to a remote P2P   user and simultaneously caches that data.  Transparency is typically   implemented using Deep Packet Inspection (DPI).  DPI products   identify and pass P2P packets to the P2P caching system so it can   cache and accelerate the traffic.   A non-transparent cache appears as a super peer; it explicitly peers   with other P2P clients.   To enable operation with existing P2P software, P2P caches directly   support P2P application protocols.  A large number of P2P protocols   are used by P2P software and hence are supported by caches, leading   to higher complexity.  Additionally, these protocols evolve over   time, and new protocols are introduced.Alimi, et al.                 Informational                    [Page 24]

RFC 6392                      DECADE Survey                 October 20114.11.1.  Applicability to DECADE   A P2P cache is an example of in-network storage for P2P systems.   However, unlike DECADE, the existence and operation of the storage   system are totally transparent to the end user.4.11.2.  Transparent P2P Caches4.11.2.1.  Data Access Interface   The data access interface allows P2P content to be cached (stored)   and supplied (retrieved) locally such that network traffic is   reduced, but it is transparent to P2P users, and P2P users implicitly   use the data access interface (in the form of their native P2P   application protocol) to store or retrieve content.4.11.2.2.  Data Management Operations   Not provided.4.11.2.3.  Data Search Capability   Not provided.4.11.2.4.  Access Control Authorization   The access control method is typically public-restricted (to any   client that is part of the P2P channel or swarm).4.11.2.5.  Resource Control Interface   Not provided.4.11.2.6.  Discovery Mechanism   The use of DPI means that no discovery mechanism is provided to P2P   users; it is transparent to P2P users.  Since DPI is used to   recognize P2P applications' private protocols, P2P cache   implementations must be updated as new applications are added and   existing protocols evolve.4.11.2.7.  Storage Mode   Object-based.  Chunks (typically, the unit of transfer among P2P   clients) of content are stored in the cache.Alimi, et al.                 Informational                    [Page 25]

RFC 6392                      DECADE Survey                 October 20114.11.3.  Non-Transparent P2P Caches4.11.3.1.  Data Access Interface   The data access interface allows P2P content to be cached (stored)   and supplied (retrieved) locally such that network traffic is   reduced.  P2P users implicitly store and retrieve from the cache   using the P2P application's native protocol.4.11.3.2.  Data Management Operations   Not provided.4.11.3.3.  Data Search Capability   Not provided.4.11.3.4.  Access Control Authorization   The access control method is typically public-restricted (to any   client that is part of the P2P channel or swarm).4.11.3.5.  Resource Control Interface   Not provided.4.11.3.6.  Discovery Mechanism   A P2P cache node behaves as if it were a normal peer in order to join   the P2P overlay network.  Other P2P users can find such a cache node   through an overlay routing mechanism and can interact with it as if   it were a normal neighbor node.4.11.3.7.  Storage Mode   Object-based.  Chunks (typically, the unit of transfer among P2P   clients) of content are stored in the cache.4.12.  Photo Sharing   There are a growing number of popular online photo-sharing (storing)   systems.  For example, the Kodak Gallery system [22] serves over   60 million users and stores billions of images [23].  Other well-   known examples of photo-sharing systems include Flickr [24] and   ImageShack [25].  There are also a number of popular bloggingAlimi, et al.                 Informational                    [Page 26]

RFC 6392                      DECADE Survey                 October 2011   services, such as Tumblr [26], that specialize in sharing large   numbers of photos as well as other multimedia content (e.g., video,   text, audio, etc.) as part of their service.  All of these in-network   storage systems utilize both free and paid subscription models.   Most photo-sharing systems are based on a traditional client-server   architecture.  However, a minority of systems also offer a P2P mode   of operation.  The client-server architecture is typically based on   HTTP, with a browser client and a Web server.4.12.1.  Applicability to DECADE   Photo sharing is a very widely used (deployed) example of in-network   storage where the end user has direct visibility and extensive   control of the system.  The typical end-user interface is through an   HTTP-based Web browser.4.12.2.  Data Access Interface   Users can read (view) and write (store) photos.4.12.3.  Data Management Operations   Users can delete previously stored photos.4.12.4.  Data Search Capability   Users can tag photos and/or organize them using sophisticated Web   photo album generators.  Users can then search for objects (photos)   matching desired criteria.4.12.5.  Access Control Authorization   The access control method for clients is typically either private or   public-unrestricted.  For example, writing (storing) to a photo blog   is typically private to the owner of the account.  However, all other   clients can view (read) the contents of the blog (i.e., public-   unrestricted).  Some photo-sharing Websites provide private access to   read photos to allow sharing with a limited set of friends.4.12.6.  Resource Control Interface   Not provided.Alimi, et al.                 Informational                    [Page 27]

RFC 6392                      DECADE Survey                 October 20114.12.7.  Discovery Mechanism   Clients usually log on manually to a central Web page for the service   and enter the appropriate information to access the desired   information.  The address to which the client connects is usually   determined by DNS using the hostname from the provided URL.4.12.8.  Storage Mode   File system (file-based).  Photos are usually stored as files.  They   can then be organized into meta-structures (e.g., albums, galleries,   etc.) using sophisticated Web photo album generators.4.13.  Usenet   Usenet is a distributed Internet-based discussion (message) system.   The Usenet messages are arranged as a set of "newsgroups" that are   classified hierarchically by subject.  Usenet information is   distributed and stored among a large conglomeration of servers that   store and forward messages to one another in so-called news feeds.   Individual users may read messages from, and post messages to, a   local news server typically operated by an ISP.  This local server   communicates with other servers and exchanges articles with them.  In   this fashion, the message is copied from server to server and   eventually reaches every server in the network [27].   Traditional Usenet as described above operates as a P2P network   between the servers, and in a client-server architecture between the   user and their local news server.  The user requires a Usenet client   to be installed on their computer and a Usenet server account   (through their ISP).  However, with the rise of Web browsers, the   Usenet architecture is evolving to be Web-based.  The most popular   example of this is Google Groups, where Google hosts all the   newsgroups and client access is via a standard HTTP-based Web   browser [28].4.13.1.  Applicability to DECADE   Usenet is a historically very important and widely used (deployed)   example of in-network storage in the Internet.  The use of this   system is rapidly declining, but efforts have been made to preserve   the stored content for historical purposes.4.13.2.  Data Access Interface   Users can read and post (store) messages.Alimi, et al.                 Informational                    [Page 28]

RFC 6392                      DECADE Survey                 October 20114.13.3.  Data Management Operations   Users sometimes have limited ability to delete messages that they   previously posted.4.13.4.  Data Search Capability   Traditionally, users could manually search through the newsgroups, as   they are classified hierarchically by subject.  In the newer Web-   based systems, there is also an automatic search capability based on   key-word matches.4.13.5.  Access Control Authorization   The access control method is either public-unrestricted or private   (to client members of that newsgroup).4.13.6.  Resource Control Interface   Not provided.4.13.7.  Discovery Mechanism   Clients usually log on manually to their Usenet accounts.  DNS may be   used to resolve hostnames to their corresponding addresses.4.13.8.  Storage Mode   File system.  Messages are usually stored as files that are then   organized hierarchically by subject into newsgroups.4.14.  Web Cache   Web cache [29] has been widely deployed by many ISPs to reduce   bandwidth consumption and Web access latency since the late 1990s.  A   Web cache can cache the Web documents (e.g., HTML pages, images)   between server and client to reduce bandwidth usage, server load, and   perceived lag.  A Web cache server is typically shared by many   clients, and stores copies of documents passing through it;   subsequent requests may be satisfied from the cache if certain   conditions are met.   Another form of cache is a client-side cache, typically implemented   in Web browsers.  A client-side cache can keep a local copy of all   pages recently displayed by a browser, and when the user returns to   one of these Web pages, the local cached copy is reused.Alimi, et al.                 Informational                    [Page 29]

RFC 6392                      DECADE Survey                 October 2011   A related protocol for P2P applications to use Web cache is HPTP   (HTTP-based Peer to Peer) [30].  It proposes sharing chunks of P2P   files/streams using HTTP with cache-control headers.4.14.1.  Applicability to DECADE   Web cache is a very widely used (deployed) example of in-network   storage for the key Internet application of Web browsing.  The   existence and operation of the storage system are transparent to the   end user in most cases.  The content caching time is controlled by   time-to-live parameters associated with the original content.  The   principle of Web caching is to speed up Web page reading by using   (the same) content previously requested by another user to service a   new user.4.14.2.  Data Access Interface   Users explicitly read from a Web cache by making requests, but they   cannot explicitly write data into it.  Data is implicitly stored in   the Web cache by requesting content that is not already cached and   meets policy restrictions of the cache provider.4.14.3.  Data Management Operations   Not provided.4.14.4.  Data Search Capability   Not provided.4.14.5.  Access Control Authorization   The access control method for clients is public-unrestricted.  It is   important to note that if content is authenticated or encrypted   (e.g., HTTPS, Secure Socket Layer (SSL)), it will not be cached.   Also, if the content is flagged as private (vs. public) at the HTTP   level by the origin server, it will not be cached.4.14.6.  Resource Control Interface   Not provided.4.14.7.  Discovery Mechanism   Web caches can be transparently deployed between a Web server and Web   clients, employing DPI for discovery.  Alternatively, Web caches   could be explicitly discovered by clients using techniques such as   DNS or manual configuration.Alimi, et al.                 Informational                    [Page 30]

RFC 6392                      DECADE Survey                 October 20114.14.8.  Storage Mode   Object-based.  Web content is keyed within the cache by HTTP Request   fields, such as Method, URI, and Headers.4.15.  Observations Regarding In-Network Storage Systems   The following observations about the surveyed in-network storage   systems are made in the context of DECADE as defined by [1].   The majority of the surveyed systems were designed for client-server   architectures and do not support P2P.  However, there are some   important exceptions, especially for some of the newer technologies   such as BranchCache and P2P cache, that do support a P2P mode of   operation.   The P2P cache systems are interesting, since they do not require   changes to the P2P applications themselves.  However, this is also a   limitation in that they are required to support each application   protocol.   Many of the surveyed systems were designed for caching as opposed to   long-term network storage.  Thus, during DECADE protocol design, it   should be carefully considered whether a caching mode should be   supported in addition to a long-term network storage mode.  There is   typically a trade-off between providing a caching mode and long-term   (and usually also reliable) storage with regards to some performance   metrics.  Note that [1] identifies issues with classical caching from   a DECADE perspective, such as the fact that P2P caches typically do   not allow users to explicitly control content stored in the cache.   Certain components of the surveyed systems are outside of the scope   of DECADE.  For example, a protocol used for searching across   multiple DECADE servers is out of scope.  However, applications may   still be able to implement such functionality if DECADE exposes the   appropriate primitives.  This has the benefit of keeping the core   in-network storage systems simple, while permitting diverse   applications to design mechanisms that meet their own requirements.   Today, most in-network storage systems follow some variant of the   authorization model of public-unrestricted, public-restricted, and   private.  For DECADE, we may need to evolve the authorization model   to support a resource owner (e.g., end user) authorization, in   addition to the network authorization.Alimi, et al.                 Informational                    [Page 31]

RFC 6392                      DECADE Survey                 October 20115.  Storage and Other Related Protocols   This section surveys existing storage and other related protocols, as   well as comments on the usage of these protocols to satisfy DECADE's   use cases.  The surveyed protocols are listed alphabetically.5.1.  HTTP   HTTP [31] is a key protocol for the World Wide Web.  It is a   stateless client-server protocol that allows applications to be   designed using the REST model.  HTTP is often associated with   downloading (reading) content from Web servers to Web browsers, but   it also has support for uploading (writing) content to Web servers.   It has been used as the underlying protocol for other protocols, such   as Web Distributed Authoring and Versioning (WebDAV).   HTTP is used in some of the most popular in-network storage systems   surveyed previously, including CDNs, photo sharing, and Web cache.   Usage of HTTP by a storage protocol implies that no extra software is   required in the client (i.e., Web-based client), as all standard Web   browsers are based on HTTP.5.1.1.  Data Access Interface   Basic read and write operations are supported (using HTTP GET, PUT,   and POST methods).5.1.2.  Data Management Operations   Not provided.5.1.3.  Data Search Capability   Not provided.5.1.4.  Access Control Authorization   All methods of access control for clients are supported: public-   unrestricted, public-restricted, and private.   The majority of Web pages are public-unrestricted in terms of reading   but do not allow any uploading of content.  In-network storage   systems range from private or public-unrestricted for photo sharing   (described inSection 4.12.5) to public-unrestricted for Web caching   (described inSection 4.14.5).Alimi, et al.                 Informational                    [Page 32]

RFC 6392                      DECADE Survey                 October 20115.1.5.  Resource Control Interface   Not provided.5.1.6.  Discovery Mechanism   Manual configuration is typically used.  Clients typically address   HTTP servers by providing a hostname, which is resolved to an address   using DNS.5.1.7.  Storage Mode   HTTP is a protocol; it thus does not define a storage mode.  However,   a non-collection resource can typically be thought of as a "file".   These files may be organized into collections, which typically map   onto the HTTP path hierarchy, creating the illusion of a file system.5.1.8.  Comments   HTTP is based on a client-server architecture and thus is not   directly applicable for the DECADE focus on P2P.  Also, HTTP offers   only a rudimentary toolset for storage operations compared to some of   the other storage protocols.5.2.  iSCSI   Small Computer System Interface (SCSI) is a set of protocols enabling   communication with storage devices such as disk drives and tapes;   Internet SCSI (iSCSI) [32] is a protocol enabling SCSI commands to be   sent over TCP.  As in SCSI, iSCSI allows an Initiator to send   commands to a Target.  These commands operate on the device level as   opposed to individual data objects stored on the device.5.2.1.  Data Access Interface   Read and write commands indicate which data is to be read or written   by specifying the offset (using Logical Block Addressing) into the   storage device.  The size of data to be read or written is an   additional parameter in the command.5.2.2.  Data Management Operations   Since commands operate at the device level, management operations are   different than with traditional file systems.  Management commands   for SCSI/iSCSI include explicit device control commands, such as   starting, stopping, and formatting the device.Alimi, et al.                 Informational                    [Page 33]

RFC 6392                      DECADE Survey                 October 20115.2.3.  Data Search Capability   SCSI/iSCSI does not provide the ability to search for particular data   within a device.  Note that such capabilities can be implemented   outside of iSCSI.5.2.4.  Access Control Authorization   With respect to access to devices, the access control method is   private.  iSCSI uses the Challenge Handshake Authentication Protocol   (CHAP) [33] to authenticate Initiators and Targets when accessing   storage devices.  However, since SCSI/iSCSI operates at the device   level, neither authentication nor authorization is provided for   individual data objects.  Note that such capabilities can be   implemented outside of iSCSI.5.2.5.  Resource Control Interface   Not provided.5.2.6.  Discovery Mechanism   Manual configuration may be used.  An alternative is the Internet   Storage Name Service (iSNS) [34], which provides the ability to   discover available storage resources.5.2.7.  Storage Mode   As a protocol, iSCSI does not explicitly have a storage mode.   However, it provides block-based access to clients.  SCSI/iSCSI   provides an Initiator with block-level access to the storage device.5.3.  NFS   The Network File System (NFS) is designed to allow users to access   files over a network in a manner similar to how local storage is   accessed.  NFS is typically used in local area networks or in   enterprise settings, though changes made in later versions of NFS   (e.g., [35]) make it easier to operate over the Internet.5.3.1.  Data Access Interface   Traditional file-system operations such as read, write, and update   (overwrite) are provided.  Locking is provided to support concurrent   access by multiple clients.Alimi, et al.                 Informational                    [Page 34]

RFC 6392                      DECADE Survey                 October 20115.3.2.  Data Management Operations   Traditional file-system operations such as move and delete are   provided.5.3.3.  Data Search Capability   The user has the ability to list contents of directories to find   filenames matching desired criteria.5.3.4.  Access Control Authorization   All methods of access control for clients are supported: public-   unrestricted, public-restricted, and private.  For example, files and   directories can be protected using read, write, and execute   permissions for the files' owner and group, and for the public   (others).  Also, NFSv4.1 has a rich ACL model allowing a list of   Access Control Entries (ACEs) to be configured for each file or   directory.  The ACEs can specify per-user read/write access to file   data, file/directory attributes, creation/deletion of files in a   directory, etc.5.3.5.  Resource Control Interface   While disk space quotas can be configured, administrative policy   typically limits the total amount of storage allocated to a   particular user.  User control of bandwidth and connections used by   remote peers is not provided.5.3.6.  Discovery Mechanism   Manual configuration is typically used.  Clients address NFS servers   by providing a hostname and a directory that should be mounted.  DNS   may be used to look up an address for the provided hostname.5.3.7.  Storage Mode   As a protocol, there is no defined internal storage mode.  However,   implementations typically use the underlying file-system storage.   Note that extensions have been defined for alternate storage modes   (e.g., block-based [36] and object-based [37]).Alimi, et al.                 Informational                    [Page 35]

RFC 6392                      DECADE Survey                 October 20115.3.8.  Comments   The efficiency and scalability of the NFS access control method are   concerns in the context of DECADE.  In particular, Section 6.2.1 of   [35] states that:      Only ACEs that have a "who" that matches the requester      are considered.   Thus, in the context of DECADE, to specify per-peer access control   policies for an object, a client would need to explicitly configure   the ACL for the object for each individual peer.  A concern with this   approach is scalability when a client's peers may change frequently,   and ACLs for many small objects need to be updated constantly during   participation in a swarm.   Note that NFSv4.1's usage of RPCSEC_GSS provides support for multiple   security mechanisms.  Kerberos V5 is required, but others, such as   X.509 certificates, are also supported by way of the Generic Security   Service Application Program Interface (GSS-API).  Note, however, that   NFSv4.1's usage of such security mechanisms is limited to linking a   requesting user to a particular account maintained by the NFS server.5.4.  OAuth   Open Authorization (OAuth) [38] is a protocol that enriches the   traditional client-server authentication model for Web resources.  In   particular, OAuth distinguishes the "client" from the "resource   owner", thus enabling a resource owner to authorize a particular   client for access (e.g., for a particular lifetime) to private   resources.   We include OAuth in this survey so that its authentication model can   be evaluated in the context of DECADE.  OAuth itself, however, is not   a network storage protocol.5.4.1.  Data Access Interface   Not provided.5.4.2.  Data Management Operations   Not provided.5.4.3.  Data Search Capability   Not provided.Alimi, et al.                 Informational                    [Page 36]

RFC 6392                      DECADE Survey                 October 20115.4.4.  Access Control Authorization   Not provided.  While similar in spirit to the WebDAV ticketing   extensions [39], OAuth instead uses the following process: (1) a   client constructs a delegation request, (2) the client forwards the   request to the resource owner for authorization, (3) the resource   owner authorizes the request, and finally (4) a callback is made to   the client indicating that its request has been authorized.   Once the process is complete, the client has a set of token   credentials that grant it access to the protected resource.  The   token credentials may have an expiration time, and they can also be   revoked by the resource owner at any time.5.4.5.  Resource Control Interface   Not provided.5.4.6.  Discovery Mechanism   Not provided.5.4.7.  Storage Mode   Not provided.5.4.8.  Comments   The ticketing mechanism requires server involvement, and the   discussion relating to WebDAV's proposed ticketing mechanism (seeSection 5.5.8) applies here as well.5.5.  WebDAV   WebDAV [40] is a protocol designed for Web content authoring.  It is   developed as an extension to HTTP (described inSection 5.1), meaning   that it can be simpler to integrate into existing software.  WebDAV   supports traditional operations for reading/writing from storage, as   well as other constructs, such as locking and collections, that are   important when multiple users collaborate to author or edit a set of   documents.5.5.1.  Data Access Interface   Traditional read and write operations are supported (using HTTP GET   and PUT methods, respectively).  Locking is provided to support   concurrent access by multiple clients.Alimi, et al.                 Informational                    [Page 37]

RFC 6392                      DECADE Survey                 October 20115.5.2.  Data Management Operations   WebDAV supports traditional file-system operations, such as move,   delete, and copy.  Objects are organized into collections, and these   operations can also be performed on collections.  WebDAV also allows   objects to have user-defined properties.5.5.3.  Data Search Capability   The user has the ability to list contents of collections to find   objects matching desired criteria.  A SEARCH extension [41] has also   been specified allowing listing of objects matching client-defined   criteria.5.5.4.  Access Control Authorization   All methods of access control for clients are supported: public-   unrestricted, public-restricted, and private.   For example, an ACL extension [42] is provided for WebDAV.  ACLs   allow both user-based and group-based access control policies   (relating to reading, writing, properties, locking, etc.) to be   defined for objects and collections.   A ticketing extension [39] has also been proposed, but has not   progressed since 2001.  This extension allows a client to request the   WebDAV server to create a "ticket" (e.g., for reading an object) that   can be distributed to other clients.  Tickets may be given expiration   times, or may only allow for a fixed number of uses.  The proposed   extension requires the server to generate tickets and maintain state   for outstanding tickets.5.5.5.  Resource Control Interface   An extension [43] allows disk space quotas to be configured for   collections.  The extension also allows WebDAV clients to query   current disk space usage.  User control of bandwidth and connections   used by remote peers is not provided.5.5.6.  Discovery Mechanism   Manual configuration is typically used.  Clients address WebDAV   servers by providing a hostname, which can be resolved to an address   using DNS.Alimi, et al.                 Informational                    [Page 38]

RFC 6392                      DECADE Survey                 October 20115.5.7.  Storage Mode   Though no storage mode is explicitly defined, WebDAV can be thought   of as providing file system (file-based) storage to a client.  A   non-collection resource can typically be thought of as a "file".   Files may be organized into collections, which typically map onto the   HTTP path hierarchy.5.5.8.  Comments   The efficiency and scalability of the WebDAV access control method   are concerns in the context of DECADE, for reasons similar to those   stated inSection 5.3.8 for NFS.  The proposed WebDAV ticketing   extension partially alleviates these concerns, but the particular   technique may need further evaluation before being applied to DECADE.   In particular, since DECADE clients may continuously upload/download   a large number of small-size objects, and a single DECADE server may   need to scale to many concurrent DECADE clients, requiring the server   to maintain ticket state and generate tickets may not be the best   design choice.  Server-generated tickets can also increase latency   for data transport operations, depending on the message flow used by   DECADE.5.6.  Observations Regarding Storage and Related Protocols   The following observations about the surveyed storage and related   protocols are made in the context of DECADE as defined by [1].   All of the surveyed protocols were primarily designed for client-   server architectures and not for P2P.  However, it is conceivable   that some of the protocols could be adapted to work in a P2P   architecture.   Several popular in-network storage systems today use HTTP as their   key protocol, even though it is not classically considered as a   storage protocol.  HTTP is a stateless protocol that is used to   design RESTful applications.  HTTP is a well-supported and widely   implemented protocol that can provide important insights for DECADE.   The majority of the surveyed protocols do not support low-latency   access for applications such as live streaming.  This was one of the   key general requirements for DECADE.   The majority of the surveyed protocols do not support any form of   resource control interface.  Resource control is required for users   to manage the resources on in-network storage systems, e.g., the   bandwidth or connections, that can be used by other peers.  Resource   control is a key capability required for DECADE.Alimi, et al.                 Informational                    [Page 39]

RFC 6392                      DECADE Survey                 October 2011   Nearly all surveyed protocols did, however, support the following   capabilities required for DECADE: ability of the user to read/write   content, some form of access control, some form of error indication,   and the ability to traverse firewalls and NATs.6.  Conclusions   Though there have been many successful in-network storage systems,   they have been designed for use cases different from those defined in   DECADE.  For example, many of the surveyed in-network storage systems   and protocols were designed for client-server architectures and not   P2P.  No surveyed system or protocol has the functionality and   features to fully meet the set of requirements defined for DECADE.   DECADE aims to provide a standard protocol for P2P applications and   content providers to access and control in-network storage, resulting   in increased network efficiency while retaining control over content   shared with peers.  Additionally, defining a standard protocol can   reduce the complexity of in-network storage, since multiple P2P   application protocols no longer need to be implemented by in-network   storage systems.7.  Security Considerations   This document is a survey of existing in-network storage systems, and   does not introduce any security considerations beyond those of the   surveyed systems.   For more information on security considerations of DECADE, see [1].8.  Contributors   The editors would like to thank the following people for contributing   to the development of this document:   - ZhiHui Lv   - Borje Ohlman   - Pang Tao   - Lucy Yong   - Juan Carlos ZunigaAlimi, et al.                 Informational                    [Page 40]

RFC 6392                      DECADE Survey                 October 20119.  Acknowledgments   The editors would like to thank the following people for providing   valuable comments to various draft versions of this document: David   Bryan, Tao Mao, Haibin Song, Ove Strandberg, Yu-Shun Wang, Richard   Woundy, Yunfei Zhang, and Ning Zong.10.  Informative References   [1]   Song, H., Zong, N., Yang, Y., and R. Alimi, "DECoupled         Application Data Enroute (DECADE) Problem Statement", Work         in Progress, October 2011.   [2]   Storage Search, "Flash Memory vs. Hard Disk Drives -- Which         Will Win?", <http://www.storagesearch.com/semico-art1.html>.   [3]   Brisken, W., "Hard Drive Price Trends", US VLBI Technical         Meeting, May 2008.   [4]   Woundy, R., "TSV P2P Efforts -- From an ISP's Perspective",         IETF 81, Quebec, Canada, July 2011,         <http://www.ietf.org/proceedings/81/slides/tsvarea-3.pdf>.   [5]   Gu, Y., Bryan, D., Yang, Y., and R. Alimi, "DECADE         Requirements", Work in Progress, September 2011.   [6]   Amazon Web Services, "Amazon Simple Storage Service         (Amazon S3)", <http://aws.amazon.com/s3/>.   [7]   Calder, B., Wang, T., Mainali, S., and J. Wu, "Windows Azure         Blob -- Programming Blob Storage", May 2009,         <http://www.microsoft.com/windowsazure/whitepapers/>.   [8]   Google, "Google Storage for Developers",         <http://code.google.com/apis/storage>.   [9]   Dropbox, "Dropbox Features", <http://www.dropbox.com/features>.   [10]  Microsoft Corporation, "BranchCache",         <http://technet.microsoft.com/en-us/network/dd425028.aspx>.   [11]  Microsoft Corporation, "Web Services Dynamic Discovery         (WS-Discovery)", April 2005, <http://specs.xmlsoap.org/ws/2005/04/discovery/ws-discovery.pdf>.Alimi, et al.                 Informational                    [Page 41]

RFC 6392                      DECADE Survey                 October 2011   [12]  Paul, S., Yates, R., Raychaudhuri, D., and J. Kurose, "The         Cache-and-Forward Network Architecture for Efficient Mobile         Content Delivery Services in the Future Internet", Innovations         in NGN: Future Network and Services, 2008.   [13]  SNIA, "Cloud Data Management Interface (CDMI)",         <http://www.snia.org/cdmi>.   [14]  Pathan, A.K. and Buyya, R., "A Taxonomy and Survey of Content         Delivery Networks", Grid Computing and Distributed Systems         Laboratory, University of Melbourne, Technical Report,         February 2007.   [15]  Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R.,         Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant Networking         Architecture",RFC 4838, April 2007.   [16]  Scott, K. and S. Burleigh, "Bundle Protocol Specification",RFC 5050, November 2007.   [17]  Named Data Networking, "Named Data Networking Home Page",         <http://www.named-data.net/>.   [18]  Named Data Networking, "Named Data Networking (NDN) Project",         <http://www.named-data.net/ndn-proj.pdf>.   [19]  Network of Information, "NetInf Overview",         <http://www.netinf.org/home/overview/>.   [20]  Anand, A., Sekar, V., and A. Akella, "SmartRE: An Architecture         for Coordinated Network-wide Redundancy Elimination",         SIGCOMM 2009.   [21]  Rhea, S., Eaton, P., Geels, D., Weatherspoon, H., Zhao, B., and         J. Kubiatowicz, "Pond: the OceanStore Prototype", FAST 2003.   [22]  Kodak, "Kodak Gallery Home Page",         <http://www.kodakgallery.com/gallery/welcome.jsp>.   [23]  Wikipedia, "Kodak Gallery",         <http://en.wikipedia.org/wiki/Kodak_Gallery>.   [24]  Flickr, "Flickr Home Page", <http://www.flickr.com>.   [25]  ImageShack, "ImageShack Home Page", <http://imageshack.us>.   [26]  Tumblr, "Tumblr Home Page", <http://www.tumblr.com>.Alimi, et al.                 Informational                    [Page 42]

RFC 6392                      DECADE Survey                 October 2011   [27]  Wikipedia, "Usenet", <http://en.wikipedia.org/wiki/Usenet>.   [28]  Google, "Google Groups", <http://groups.google.com>.   [29]  Huston, G., Telstra, "Web Caching", The Internet Protocol         Journal Volume 2, No. 3.   [30]  Shen, G., Wang, Y., Xiong, Y., Zhao, B., and Z-L. Zhang, "HPTP:         Relieving the Tension between ISPs and P2P", 6th International         Workshop on Peer-To-Peer Systems (IPTPS2007).   [31]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,         Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --         HTTP/1.1",RFC 2616, June 1999.   [32]  Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M., and E.         Zeidner, "Internet Small Computer Systems Interface (iSCSI)",RFC 3720, April 2004.   [33]  Simpson, W., "PPP Challenge Handshake Authentication Protocol         (CHAP)",RFC 1994, August 1996.   [34]  Tseng, J., Gibbons, K., Travostino, F., Du Laney, C., and J.         Souza, "Internet Storage Name Service (iSNS)",RFC 4171,         September 2005.   [35]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network         File System (NFS) Version 4 Minor Version 1 Protocol",RFC 5661, January 2010.   [36]  Black, D., Fridella, S., and J. Glasgow, "Parallel NFS (pNFS)         Block/Volume Layout",RFC 5663, January 2010.   [37]  Halevy, B., Welch, B., and J. Zelenka, "Object-Based Parallel         NFS (pNFS) Operations",RFC 5664, January 2010.   [38]  Hammer-Lahav, E., Ed., "The OAuth 1.0 Protocol",RFC 5849,         April 2010.   [39]  Ito, K.,"Ticket-Based Access Control Extension to WebDAV",         Work in Progress, October 2001.   [40]  Dusseault, L., Ed., "HTTP Extensions for Web Distributed         Authoring and Versioning (WebDAV)",RFC 4918, June 2007.   [41]  Reschke, J., Ed., Reddy, S., Davis, J., and A. Babich, "Web         Distributed Authoring and Versioning (WebDAV) SEARCH",RFC 5323, November 2008.Alimi, et al.                 Informational                    [Page 43]

RFC 6392                      DECADE Survey                 October 2011   [42]  Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web         Distributed Authoring and Versioning (WebDAV)         Access Control Protocol",RFC 3744, May 2004.   [43]  Korver, B. and L. Dusseault, "Quota and Size Properties         for Distributed Authoring and Versioning (DAV) Collections",RFC 4331, February 2006.Authors' Addresses   Richard Alimi (editor)   Google   EMail: ralimi@google.com   Akbar Rahman (editor)   InterDigital Communications, LLC   EMail: Akbar.Rahman@InterDigital.com   Yang Richard Yang (editor)   Yale University   EMail: yry@cs.yale.eduAlimi, et al.                 Informational                    [Page 44]